JP2009117074A - Fuel cell system - Google Patents

Abstract

A fuel cell system capable of accurately estimating IV characteristics of a fuel cell is provided.
A learning unit 84 obtains a difference between an IV characteristic estimation line generated by an IV characteristic estimation line creation unit 83 and an actual operation point at the present time, and the obtained difference (that is, voltage deviation) is determined as a direct current. It feeds back the voltage drop due to the resistance and the change in electromotive voltage. Specifically, the learning unit 84 searches the gain determination map MP1 using the current output current of the fuel cell as a search key. In the gain determination map MP1, the ratio of the feedback gain as the DC resistance and the feedback gain as the change in electromotive voltage is set to be different according to the output current of the fuel cell. The IV characteristics of the battery can be estimated with high accuracy.
[Selection] Figure 5

Description

  The present invention relates to a fuel cell system, and more particularly to a fuel cell system that controls output power in accordance with the operating state of the fuel cell.

  In the present age when the future image of an oil-dependent automobile society is concerned, the spread of automobiles equipped with fuel cells that use hydrogen as fuel is expected. A fuel cell has a stack structure in which cells are stacked in series, and generates electricity using an electrochemical reaction between a fuel gas containing hydrogen supplied to the anode and an oxidizing gas containing oxygen supplied to the cathode. Yes.

  The fuel cell has various restrictions when starting up as compared with other power sources. The power generation efficiency of such a fuel cell decreases due to a decrease in temperature or poisoning of the electrode catalyst, and there may be a case where a desired voltage / current cannot be supplied and the device cannot be started.

  In view of such circumstances, when starting the fuel cell, an operation different from the normal operation, that is, at least one of the fuel gas supplied to the anode and the oxidizing gas supplied to the cathode is set in a deficient state, An operation for increasing the temperature of the fuel cell and recovering the poisoning of the electrode catalyst (hereinafter referred to as a refresh operation) is performed by increasing the overvoltage of the part to generate further heat (see, for example, Patent Document 1 below) ).

Special table 2003-504807

  By the way, the current / voltage characteristic (IV characteristic) of the fuel cell is not constant, and varies greatly depending on the output current of the fuel cell, the operation state of the fuel cell (whether it is in the normal operation state or the refresh operation state), and the like. If the output power of the fuel cell is controlled without taking such fluctuations into account, there are concerns about problems such as overcharging the secondary battery.

  The present invention has been made in view of the above-described circumstances, and an object thereof is to provide a fuel cell system capable of accurately estimating the IV characteristics of a fuel cell.

  In order to solve the above-described problems, a fuel cell system according to the present invention includes a fuel cell, an output current at an actual operation point of the fuel cell, a current / voltage detection unit that detects an output voltage, and a current of the fuel cell. An estimation means for estimating a voltage characteristic, a voltage deviation detection means for detecting a voltage deviation generated between the estimated current-voltage characteristic of the fuel cell and the output voltage at the detected actual operation point, and detection Feedback control means that feeds back the voltage deviation to at least one of the voltage change amount corresponding to the resistance of the fuel cell and the change amount of the electromotive voltage of the fuel cell, and according to the detected output current of the fuel cell A feedback gain ratio of the voltage deviation to be fed back to at least one of the voltage change amount of the resistance and the change amount of the electromotive voltage. Characterized by comprising a down control unit.

  According to such a configuration, the ratio of the feedback gain of the voltage deviation to be fed back to at least one of the voltage change amount for the resistance and the change amount of the electromotive voltage is changed according to the detected output current of the fuel cell. The ratio of the feedback gain of the voltage deviation according to the output current is changed, for example, when the output current is large, the direct current resistance is likely to change due to the large change in the water content in the electrolyte membrane of the fuel cell, while the output is This is because if the current is small, the contribution as a direct current resistance is too small to follow, and a value significantly different from the actual direct current resistance is set. Therefore, by performing the above control, it is possible to estimate the IV characteristic of the fuel cell with higher accuracy than in the past, thereby suppressing the deviation between the actual IV characteristic of the fuel cell and the IV characteristic estimation line. It becomes possible.

  Here, in the above configuration, a plurality of current regions having different feedback gain ratios are set in the gain control means, and the gain control means is configured to detect the output current of the fuel cell as described above. It is determined which one of the plurality of current regions belongs, and a feedback gain ratio of the voltage deviation to be fed back to at least one of the voltage change amount of the resistance and the change amount of the electromotive voltage is changed according to the determination result. Embodiments are preferred.

  Further, the above configuration further includes a stoichiometric ratio detecting means for detecting a stoichiometric ratio of the oxidizing gas supplied to the fuel cell, and the gain control means is configured to detect the resistance component according to the detected stoichiometric ratio. The aspect of changing the feedback gain ratio of the voltage deviation fed back to at least one of the voltage change amount and the electromotive voltage change amount may be employed.

  As described above, according to the present invention, it is possible to accurately estimate the IV characteristics of the fuel cell.

  Embodiments according to the present invention will be described below with reference to the drawings.

A. Embodiment A-1. Configuration FIG. 1 is a schematic configuration of a vehicle equipped with a fuel cell system 100 according to the present embodiment. In the following description, a fuel cell vehicle (FCHV) is assumed as an example of the vehicle, but the present invention can also be applied to an electric vehicle and a hybrid vehicle. Further, the present invention can be applied not only to vehicles but also to various moving bodies (for example, ships, airplanes, robots, etc.), stationary power sources, and portable fuel cell systems.

  The fuel cell 40 is means for generating electric power from the supplied reaction gas (fuel gas and oxidant gas), and various types of fuel cells such as a solid polymer type, a phosphoric acid type, and a molten carbonate type can be used. it can. The fuel cell 40 has a stack structure in which a plurality of single cells including MEAs and the like are stacked in series. The output voltage (hereinafter referred to as FC voltage) and output current (hereinafter referred to as FC current) at the actual operation point of the fuel cell 40 are detected by the voltage sensor 140 and the current sensor 150, respectively. A fuel gas such as hydrogen gas is supplied from the fuel gas supply source 10 to the fuel electrode (anode) of the fuel cell 40, while an oxidizing gas such as air is supplied from the oxidizing gas supply source 70 to the oxygen electrode (cathode). Supplied.

The fuel gas supply source 10 includes, for example, a hydrogen tank, various valves, and the like, and controls the amount of fuel gas supplied to the fuel cell 40 by adjusting the valve opening, the ON / OFF time, and the like.
The oxidizing gas supply source 70 includes, for example, an air compressor, a motor that drives the air compressor, an inverter, and the like, and adjusts the amount of oxidizing gas supplied to the fuel cell 40 by adjusting the rotational speed of the motor.

  The battery 60 is a chargeable / dischargeable secondary battery, and is composed of, for example, a nickel metal hydride battery. Of course, instead of the battery 60, a chargeable / dischargeable capacitor (for example, a capacitor) other than the secondary battery may be provided. The battery 60 and the fuel cell 40 are connected in parallel to an inverter 110 for a traction motor, and a DC / DC converter 130 is provided between the battery 60 and the inverter 110.

  The inverter 110 is, for example, a pulse width modulation type PWM inverter, which converts DC power output from the fuel cell 40 or the battery 60 into three-phase AC power in accordance with a control command given from the control device 80, and a traction motor 115. To supply. The traction motor 115 is a motor for driving the wheels 116 </ b> L and 116 </ b> R, and the rotation speed of the motor is controlled by the inverter 110.

  The DC / DC converter 130 is a full-bridge converter configured by, for example, four power transistors and a dedicated drive circuit (all not shown). The DC / DC converter 130 functions to step up or step down the DC voltage input from the battery 60 and output it to the fuel cell 40 side, and step up or step down the DC voltage input from the fuel cell 40 or the like to the battery 60 side. It has a function to output. Further, charging / discharging of the battery 60 is realized by the function of the DC / DC converter 130.

  An auxiliary machine 120 such as a vehicle auxiliary machine or an FC auxiliary machine is connected between the battery 60 and the DC / DC converter 130. The battery 60 is a power source for these auxiliary machines 120. The vehicle auxiliary equipment refers to various electric power devices (lighting equipment, air conditioning equipment, hydraulic pump, etc.) used during vehicle operation, and the FC auxiliary equipment is used to operate the fuel cell 40. It refers to various power devices (pumps for supplying fuel gas and oxidizing gas, etc.).

  The control device 80 includes a CPU, a ROM, a RAM, and the like. The voltage sensor 140 that detects the FC voltage, the current sensor 150 that detects the FC current, the temperature sensor 50 that detects the temperature of the fuel cell 40, and the charging of the battery 60. Each part of the system is centrally controlled based on each sensor signal input from an SOC sensor that detects the state, an accelerator pedal sensor that detects the opening of the accelerator pedal, and the like. Further, the control device 80 estimates the IV characteristic with higher accuracy than before by estimating the voltage drop of the fuel cell 40 for each factor.

<IV characteristic estimation process>
2 and 3 are explanatory diagrams for explaining a conventional IV characteristic estimation process. 2 and 3, the estimation line of the voltage drop (activation overvoltage) due to the activation polarization as the IV characteristic estimation material is indicated by a one-dot chain line, the IV characteristic estimation line is indicated by a solid line, and the voltage drop due to DC resistance The estimated line is indicated by a two-dot chain line. 2 and 3, the vertical axis and the horizontal axis represent the FC voltage and the FC current, respectively, and the intercept of the vertical axis represents the electromotive force (electromotive voltage) Ve of the fuel cell.

  As shown in FIG. 2, the conventional fuel cell system represents the electromotive force Ve and the activation overvoltage of the fuel cell as fixed values. For this reason, when the FC voltage and the FC current are detected by the voltage sensor and the current sensor and the actual operation point (Ifc1, Vfc1) of the fuel cell is obtained, the difference between the FC voltage indicated by the actual operation point and the activation overvoltage is obtained. Were all judged to be a voltage drop due to DC resistance (see FIG. 3).

  However, if the difference between the FC voltage and the activation voltage indicated at the actual operation point as described above is determined as a voltage drop due to the DC resistance, and the estimated value of the voltage drop due to the DC resistance is moved with a time constant, the IV characteristic estimation line A large discrepancy occurs between the actual operation point and the actual operation point.

  In order to suppress such a divergence, in this embodiment, the voltage drop caused by the operation is divided into (1) a voltage drop that is not proportional to the current, and (2) a voltage drop that is proportional to the current (voltage drop due to DC resistance). (3) The voltage drop corresponding to the change in electromotive voltage is roughly divided into three, and the IV characteristics of the fuel cell are estimated based on these (see FIG. 4). Here, in FIG. 4, the voltage drop corresponding to the change in electromotive voltage is indicated by a thick broken line. In the present embodiment, the voltage drop for polarization means a voltage drop for activation polarization and a voltage drop for concentration polarization. However, for convenience of explanation, in the following, (1) an activation voltage (voltage drop caused by activation polarization) is assumed as a voltage drop corresponding to polarization not proportional to the current.

<Countermeasure>
First, the feed forward amount of the activation overvoltage and the DC resistance estimation value is given. Here, the feed forward amount of the activation overvoltage may be a fixed value set in advance at the time of manufacture and shipment, or may be a mapped value. Furthermore, the measured impedance value obtained in advance through experiments or the like may be used for the feedforward portion of the estimated DC resistance value. Next, the remaining voltage drop is fed back while switching the gain to the voltage change caused by the DC voltage drop.

FIG. 5 is a functional block diagram relating to the IV characteristic estimation function of the control device 80.
The control device 80 includes an FF term generation unit 81, an IV characteristic estimation line creation unit 83, and a learning unit 84.

  The FF term generation unit 81 is activated based on a map (FF map) for providing a feedforward amount of the activation overvoltage and the DC resistance estimated value stored at the time of manufacture and shipment, and the temperature of the fuel cell at the time point. Derive the feedforward component of the overvoltage and DC resistance estimate. Then, the FF term generation unit 81 notifies the derived feedforward amount to the IV characteristic estimation line creation unit 83.

  The IV characteristic estimation line creation unit 83 calculates a voltage drop element (hereinafter referred to as a residual voltage drop element) excluding the activation overvoltage and the feedforward amount of the DC resistance estimation value, and creates an IV characteristic estimation line. Specifically, the IV characteristic estimation line creation unit (current / voltage detection means) 83 first obtains the actual operation point (Ifc1, Vfc1) of the fuel cell 40 at the present time (see FIG. 6).

  Then, the IV characteristic estimation line creation unit 83 obtains a voltage drop that combines the change in the electromotive voltage and the remainder of the voltage drop due to the DC resistance as a residual voltage drop element (see FIG. 7). The IV characteristic estimation line creation unit 83 uses the estimation line created from the feed forward of the activation overvoltage and the DC resistance estimation value, and the remaining ΔV (= Ve−Ve) of the change in the electromotive voltage and the voltage drop due to the DC resistance. After obtaining '), an IV characteristic estimation line as shown in FIG. 7 is generated. In FIG. 7, the IV characteristic estimation line is indicated by a solid line, the activation overvoltage estimation line is indicated by a one-dot chain line, and the estimation line for the voltage drop due to the DC resistance is indicated by a two-dot chain line.

  The learning unit (voltage deviation detection means) 84 obtains a difference between the IV characteristic estimation line generated by the IV characteristic estimation line creation unit 83 and the actual operation point at the present time, and obtains the obtained difference (ie, voltage deviation). Is fed back to the voltage drop due to the DC resistance (voltage change amount for the resistance) and electromotive voltage change amount (electromotive voltage change amount).

  More specifically, the learning unit (gain control means) 84 searches the gain determination map MP1 using the current output current Ifc1 of the fuel cell 40 as a search key. In the gain determination map MP1, a feedback gain as a voltage drop due to a DC resistance and a feedback gain as an electromotive voltage change are registered for each set current region. FIG. 8 is a diagram illustrating registered contents of the gain determination map MP1. As shown in FIG. 8, in this embodiment, three current regions of 0 (A), 0 to 50 (A), and 50 (A) or more are set, and a voltage drop due to a DC resistance is set for each set current region. Feedback gains α1, α2 (> α1), α3 (> α2) as minutes, and feedback gains β1, β2 (<β1), β3 (<β2) as electromotive voltage changes are registered.

As shown in FIG. 8, as the output current Ifc1 (that is, the load) increases, the feedback gain (feedback gain ratio) as a DC resistance component is set larger, while as the output current Ifc decreases, the electromotive voltage changes. Set a large feedback gain (ratio of feedback gain) as a minute.
This is because when the output current Ifc1 is large, the change in the water content in the electrolyte membrane of the fuel cell 40 is large, so that the direct current resistance is likely to change. On the other hand, when the output current Ifc1 is small, the direct current resistance is fed back. This is because the contribution is too small to follow, and a value greatly different from the actual DC resistance is set. Note that the range and number of current regions to be set can be arbitrarily changed.

  When the learning unit (feedback control unit, gain control unit) 84 acquires each feedback gain (for example, α2, β2) corresponding to the current output current Ifc1 of the fuel cell 40 from the gain determination map MP1, the acquired feedback gains are obtained. Is used to feed back the voltage drop due to the DC resistance and the change in the electromotive voltage, thereby correcting the IV characteristic estimation line. As described above, the IV characteristics of the fuel cell can be accurately estimated by changing the ratio of the feedback gain as the direct current resistance and the feedback gain as the change in electromotive voltage according to the output current Ifc1 of the fuel cell 40. It becomes possible. Hereinafter, the IV characteristic estimation process executed by the control device 80 will be described with reference to FIG.

A-2. Explanation of Operation FIG. 9 is a flowchart showing IV characteristic estimation processing.
First, the FF term generation unit 81 derives the feed forward amount of the activation overvoltage and the DC resistance estimation value using the FF map during the system operation (step S100). Then, the FF term generation unit 81 notifies the derived feedforward amount to the IV characteristic estimation line creation unit 83.

  The IV characteristic estimation line creation unit 83 obtains a voltage drop that combines the change in the electromotive voltage and the remainder of the voltage drop due to the DC resistance as a residual voltage drop element, and then generates an IV characteristic estimation line as shown in FIG. (Step S200).

  Thereafter, the learning unit 84 obtains a difference between the IV characteristic estimation line generated by the IV characteristic estimation line creation unit 83 and the actual operation point at the present time, and the obtained difference (that is, voltage deviation) is determined by the DC resistance. It feeds back the voltage drop (voltage change amount of resistance) and electromotive voltage change (electromotive voltage change amount).

  More specifically, the learning unit 84 searches the gain determination map MP1 using the current output current Ifc1 of the fuel cell 40 as a search key. When the learning unit 84 acquires each feedback gain (for example, α2, β2) corresponding to the current output current Ifc1 of the fuel cell 40 from the gain determination map MP1 (step S300), the learning unit 84 uses the acquired feedback gains to perform direct current. By feeding back the voltage drop due to the resistance and the change in the electromotive voltage (step S400), the IV characteristic estimation line is corrected, and the process ends.

  As described above, according to the present embodiment, the ratio of the feedback gain as the DC resistance and the feedback gain as the change in electromotive voltage is changed according to the output current Ifc1 of the fuel cell 40. As a result, it is possible to estimate the IV characteristics of the fuel cell with higher accuracy than in the prior art, thereby suppressing the deviation between the actual IV characteristics of the fuel cell and the IV characteristic estimation line.

  In the present embodiment described above, the activation overvoltage (voltage drop caused by activation polarization) is not particularly mentioned. However, for example, the change over time (time) of the fuel cell 40 is added to the feedforward term of the activation overvoltage. Parameter) and temperature change may be included. Thereby, the IV characteristic of the fuel cell can be estimated with higher accuracy.

  In the present embodiment described above, the ratio of both the gain of the feedback gain as the DC resistance and the feedback gain as the change in electromotive voltage is changed according to the output current Ifc1, but either one of the feedback gains (for example, Only the feedback gain as the DC resistance component) may be changed. This also applies to the application examples shown below.

B. Application example <Application example 1>
In the above-described embodiment, the ratio of each feedback gain is changed according to the output current Ifc1 of the fuel cell 40. However, instead of the output current Ifc1 of the fuel cell 40, the operating state of the fuel cell 40 (that is, the normal operation). Alternatively, the ratio of each feedback gain may be changed according to whether the operation is a refresh operation.

  Here, the operating state of the fuel cell 40 can be determined based on the amount of reaction gas (here, oxidizing gas) supplied to the fuel cell 40 (the amount of supply gas per unit time). Specifically, the learning unit (stoichiometric ratio detection means) 84 determines whether or not the air stoichiometric ratio at the time is equal to or greater than a set threshold value (hereinafter, “1” is assumed), and sets the air stoichiometric ratio to 1 or more. If it is, it is determined that it is in a normal operation state, and if the air stoichiometric ratio is set to less than 1, it is determined that it is in a refresh operation state. The setting threshold can be arbitrarily set / changed according to the system design or the like.

FIG. 10 is a diagram illustrating the registered contents of the gain determination map MP2 according to the application example 1. In the application example 1, the gain determination map MP2 is stored in the learning unit 84.
As shown in FIG. 10, in this embodiment, a stoichiometric ratio of 1 or more (normal operation) and a stoichiometric ratio of less than 1 (refresh operation) are set. α1 ′ and α2 ′ (> α1 ′) and feedback gains β1 ′ and β2 ′ (<β1 ′) as changes in electromotive voltage are registered.

  The learning unit 84 detects whether or not the air stoichiometric ratio at the time is 1 or more by detecting the amount of oxidizing gas (such as the amount of gas supplied per unit time) supplied to the fuel cell 40 at a predetermined timing. Judgment is made, and each feedback gain (for example, α2 ′, β2 ′) corresponding to the current air stoichiometric ratio is acquired from the gain determination map MP2. Then, the learning unit 84 corrects the IV characteristic estimation line by using the obtained feedback gains and feeding back to the voltage drop due to the DC resistance and the change in electromotive voltage. Thus, according to the stoichiometric ratio of the oxidizing gas supplied to the fuel cell 40 (in other words, the operating state of the fuel cell 40), the feedback gain as the DC resistance and the feedback gain as the change in electromotive voltage are changed. By changing the ratio, it is possible to accurately estimate the IV characteristics of the fuel cell.

In the above-described embodiment, a fixed value set in advance at the time of manufacture and shipment is assumed as the feedforward for the estimated DC resistance value. However, an impedance measurement value may be used.
Here, FIG. 11 is a diagram schematically showing the result of impedance measurement by the AC impedance method on a complex plane, with the ordinate representing the imaginary part and the abscissa representing the real part.

  When the impedance of the fuel cell 40 is measured under a predetermined condition and the locus of the impedance accompanying the frequency change is plotted on a complex plane (Cole-Cole plot), an impedance curve as shown in FIG. 11 is obtained. Such impedance measurement is performed intermittently or continuously during the operation of the system. Then, the real part of the measured impedance (measurement impedance) is set as the DC resistance estimated value Re, and the DC resistance estimated value Re is multiplied by the FC current detected by the current sensor 150 to obtain the voltage drop due to the DC resistance. As described above, the measured impedance value may be used as a feedforward component of the estimated DC resistance value.

It is a figure which shows the principal part structure of the fuel cell system which concerns on this embodiment. It is explanatory drawing explaining the estimation process of conventional IV characteristic. It is explanatory drawing explaining the estimation process of conventional IV characteristic. It is explanatory drawing explaining each voltage drop part which arises by driving | operation. It is a functional block diagram concerning an IV characteristic estimation function. It is explanatory drawing explaining the derivation process of a voltage drop. It is explanatory drawing explaining the production | generation process of IV characteristic estimation line. It is the figure which illustrated the contents of registration of gain determination map MP1. It is a flowchart which shows IV characteristic estimation processing. It is the figure which illustrated the registered contents of gain determination map MP2. It is the figure which illustrated the impedance curve.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 ... Fuel gas supply source, 40 ... Fuel cell, 50 ... Temperature sensor, 60 ... Battery, 70 ... Oxidation gas supply source, 80 ... Control apparatus, 81 ... FF Term generation unit, 83 ... IV characteristic estimation line creation unit, 84 ... learning unit, MP1, MP2 ... gain determination map, 110 ... inverter, 115 ... motor, 116L, 116R ... Wheel, 130 ... DC / DC converter, 140 ... voltage sensor, 150 ... current sensor, 100 ... fuel cell system.

Claims (3)

A fuel cell;
Output current at the actual operation point of the fuel cell, current / voltage detection means for detecting the output voltage,
Estimating means for estimating current / voltage characteristics of the fuel cell;
A voltage deviation detecting means for detecting a voltage deviation generated between the estimated current-voltage characteristic of the fuel cell and the output voltage at the detected actual operation point;
Feedback control means for feeding back the detected voltage deviation to at least one of a voltage change amount corresponding to the resistance of the fuel cell and an electromotive voltage change amount of the fuel cell;
Gain control means for changing a feedback gain ratio of the voltage deviation to be fed back to at least one of the voltage change amount of the resistance and the change amount of the electromotive voltage according to the detected output current of the fuel cell. A fuel cell system comprising:   A plurality of current regions having different feedback gain ratios are set in the gain control unit, and the gain control unit determines which of the plurality of current regions the output current of the fuel cell to be detected belongs to. 2. The feedback gain ratio of the voltage deviation fed back to at least one of the voltage change amount of the resistance and the change amount of the electromotive voltage is changed in accordance with the determination result. Fuel cell system. A stoichiometric ratio detecting means for detecting a stoichiometric ratio of the oxidizing gas supplied to the fuel cell;
The gain control unit changes a feedback gain ratio of the voltage deviation to be fed back to at least one of a voltage change amount of the resistance and a change amount of the electromotive voltage according to a detected stoichiometric ratio. The fuel cell system according to claim 1.

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